90s teen novel about an alien invasion in a small farm town. Showdown in the school at the end of the novel

I read this story in the early 2000's, found it in a hospital gift shop. The story centered around a small town where the kids begin to notice that the adults are acting strangely. I remember there being some kids that lived on farms. Only the kids knew about the invasion and no one believed them. As the aliens realized that the kids were on to them, they were creating accidents to kill the kids. I remember one part where one of the kids died because he was run over by a tractor. There might have been a reaction from the aliens to water, if I remember correctly. The final showdown took place in a school (the high school I think?) where the kids were able to defeat the aliens. The kids were not high school-aged, more like early Tweens-teens. The cover was a little on the cheesy side, showing the kids with the town in the background, and the green alien lights.

This book has sentimental value. I've been looking for years, but can't find much without a title. Thanks.